This study is concerned with the detailed mechanism of myosin ATPase and the relationship between the elementary processes of this reaction and the contractile events in muscle. These problems will be investigated by stopped-flow and nanosecond fluorimetry using 1,N6-ethenoadenosinephosphates and other fluorescent probes. In particular, the method of excited state energy transfer will be extensively used to monitor complex formation and isomerization in the kinetic studies as well as to determine proximity relationships in the active site region involving the enzyme-substrate complex. The combination of transient kinetic and spectroscopic approaches using the same signal is expected to provide a detailed picture of the molecular behavior of the enzyme. These experimental results will provide the basis for computer-modeling studies which will help clarify the relationship of enzymatic activity to energy transduction occurring during contraction.